A sylphon is an old name for a cylindrically symmetrical metal bellows.
[1] A sylphon, or bellows, is used, among other purposes, to transfer motion through the wall of a vacuum chamber.
It can also be used as a flexible coupling to transfer rotary motion between shafts.
The sylphon was invented in the early 1900s by meteorologist Weston Fulton (1871–1946), who named it for the sylphs of Western mythology.
[2] Also, a trade name used by Johnson Controls for pneumatically operated valves and damper actuators utilizing a metal bellows, they were rendered obsolete in the 1930s and 40s.